Rotary apparatus for treating particulate material

ABSTRACT

Apparatus for treating particulate material comprises a multiplicity of tubes mounted within a rotating shell. The material and a treating gas flow together through the tubes, while a heating or cooling fluid is conducted through a closed chamber surrounding the tubes for heat exchange with the tube walls, and thus with the material. The material is aerated as it flows through the tubes by gentle mechanical tumbling agitation. A flow-control dam near the outlet end of each tube provides a controlled fill of each tube and ensures a controlled retention time for the material.

11 1 1 1 United States act 1191 [11 3,765,12 Fischer 1 Uct. 16, 1973[54] ROTARY APPARATUS FOR TREATING 1,358,313 11/1920 Hero 34 136PARTICULATE MATERIAL 1,477,823 12/1923 Grindle..... 432/107 3,228,670l/l966 Moklebust.... 432/118 [75] Inventor: John J- Fisch r, E Str b rg.3,490,754 1 1970 Bauer 34 109 [73] Assignee: The Patterson-Kelley Co.Inc., East Primary Emmi'fer carron Dority,

stroudsburg, pa Assistant Examiner-Larry I. Schwartz Attorney-GranvilleM. Brumbaugh et a1. [22] Filed: Sept. 21, 1972 [21] Appl. No.: 291,077[57] ABSTRACT Apparatus for treating particulate material comprises 52us. c1. 34/136, 432/107 34/138 multiplidty 0f tubes mounted within amating Shell 34/141 The material and a treating gas flow togetherthrough 51 1m. (:1. F26b 11/02 the tubes while a heating coding fluid isConducted [58] Field 6: Search 34/128, 136 13s, thmugh a chambersufmunding the tubes 34/140 141 432/107 heat exchange with the tubewalls, and thus with the material. The material is aerated as it flowsthrough [56] References Cited the tubes by gentle mechanical tumblingagitation. A

flow-control dam near the outlet end of each tube pro- UNITED STATESPATENTS vides a controlled fill of each tube and ensures a cong; g 1

trolled retention time for the material. umey 910,071 1] 1909 Kohn etal. 34/133 23 Claims, 20 Drawing Figures PATENTED BUT I 6 I975 SHEET IN4 PATENTEB BUT I 61975 SHEET 2 [IF 4 PATENIEO 1 61915 3.765.1 O2

sum 3 or 4 BACKGROUND OF THE INVENTION This invention relates toapparatus for treating particulate material and, in particular, toapparatus having considerable versatility and appropriate for varioususes, such as heating, cooling or drying particulate materials orpromoting chemical reactions between particulate materials and gases.

Various types of equipment have been proposed and used for heating,cooling and drying particulate materials and for reacting particulatematerials with gases and vapors. For the most part, such equipment isdesigned to provide maximum exposure of the material surfaces to atreating gas. In recent years, fluidized bed treatment, a process thatinvolves controlled, partial suspension of material in a vertical bed,by an upwardly flow-, ing gas, has been emphasized in. development anduse. In a related, though somewhat different, technique which isemployed, for example, in so-called flash dryers, the material tobetreated is conveyed in a concurrent, high speed flow of gas. Bothfluidized bed and concurrent flow treatments require carefully designedand highly specialized equipment tailored to the specific requirementsof the process. Moreover, they are effective only with a relativelynarrow range of materials having only a very narrow range of particlesizes.

The processes are difficult to control and, in general,

have not'been successful where a high precision output is required.

Fluidized bed drying processes'require specific air flow velocities thatvary with particle size and density. Fine particles that enter above thebed meet almost saturated gas having almost no drying capability and areblown across the top of the bed to the outlet in an un dry" state. Thelargest particles tend to settle to and remain at the bottom of the bedwhere they are subject to overheating and consequent damage. Somematerials lose density by swelling when wet and tend to float across thetop of the bed to the outletjwithout drying. Sticky materials aretotally unsuited to fluidized bed treatment, since they tend toagglomerate in the bed, thus changing effective particle sizes anddestroying fluidization under the gas velocity applicable to theoriginal particle size.

Flash drying processes are useful only with materials having primarilysurface moisture, little absorbed or bound" moisture, fine particle sizeand, preferably,

nearly uniform particle size. With suitable material,

drying occurs in a matter of seconds. Such rapid drying, however, makesit difficult to obtain a' product output having uniform dryness.

Various types of conveyor and rotary material treating devices have beensuggested or employed, these types being preferable or even necessaryfor processes involving wide. particle size variations, considerablebound moisture, friable materials (usually limited to conveyor typesystems) or other material characteristics that make fluidized bed andconcurrent flow processes inappropriate. The rotary equipment generallyemploys large diameter shells equipped with wallmounted lifting vanesthat drop the material across a concurrent or countercurrent gas flow.Often the distance that the particles must drop is considerable, thusmaking many rotary devices unsuitable for treating fragile or friablematerials. Gas flow velocities are usually very low, since particleentrainment and premature ejection of material by gas entrainment mustbe limited as much as possible to ensure an acceptable product.

SUMMARY OF THE INVENTION There is provided, in accordance with thepresent invention, an apparatus for treating particulate materials,e.g., heating, cooling, drying or gas (or vapor) reaction, that ishighly versatile as to use and very efficient, especially if carefullydesigned and properly controlled, and, most importantly, may be readilycontrolled to produce a uniform, precisely conditioned output. Althoughit is inherently slower than concurrent gas flow equipment, the slowprocessing rate leads to good control in that drying of the materialtakes place over a period of minutes, rather than seconds. Thus, it iscapable of effectively treating materials having a wide range ofparticle sizes (i.e., broad size distribution) and relatively largeparticle sizes, materials that are, at best, difficult effectively totreat by fluidized bed or concurrent gas flow techniques because of thecontrol problems inherent in such techniques. The equipment can handleabrasive materials, which are troublesome in any type of process, withlittle wear of the equipment or other difficulties.

The apparatus comprises a cylindrical shell mounted for rotation aboutits axis and appropriately driven in rotation, fixed end covers closingthe ends of the shells, and a pair of tube sheets carrying amultiplicity of tubes that extend along the major part of the length ofthe shell, preferably parallel to the shell axis. The upstream tubesheet and the upstream cover define an inlet zone, and the downstreamtube sheet and end cover form an outlet zone. The space between the tubesheets and outside the tubes is a closed chamber and is equipped forsupply and flow of a heating or cooling fluid'providing heat exchangewith the tube walls, and thus with the material. I

The material to be treated and a treating gas (or vapor) are introducedat controlled rates to the inlet zone, flow together through the tubes,and are with-- the material moves along the tube and promote heattransfer between the material and the tube walls, the agitating devicesin each tube, and the gases flowing through the tubes. The balancebetween heat transfer by conduction between the particles and thesurfaces they contact and transfer by convection and conduction betweenthe particles and flowing gases is provided, among other things, byvarying the temperatures and flow rates of the gas flowing with thematerial and the heating or cooling fluid in the closed chambersurrounding the tubes. Other parameters of the system, such asthroughput rate, the extent of aeration of the material, the degree ofheat transfer to or from the material by conduction are also readilyvaried by adjusting the feed rate of the material, the rate of rotationof the shell, the design of the agitating system and the inclination ofthe shell axis. These matters are discussed below in more detail.

An important aspect of the control of the equipment is the ability tocontrol the till (i.e., the amount of material contained in) of eachtube. Fill is controlled by a flow-control dam element adjacent or atthe downstream end of each tube. The dam element is a member thatextends circumferentially, either substantially perpendicular to orhelically of the tube axis, of the inner wall of the tube and inwardlyfrom the tube wall a uniform distance. The dam element may be a flatannular disc witha circular, centered outlet opening, a strip ofmaterial installed on a generally helical-shaped path (a screw form) andextending in from the wall a uniform distance to define, as viewed fromthe tube end, a circular hole centered on the tube axis or sections ofannular discs in a spaced and staggered arrangement, with endsoverlapping. Any'of these forms of dam element ensures the retention ofa layer of material in thetube, a factor that has been found to becritical to the ability to control the throughput and prevent variationsin the linear flow rate of material down the tube and the blowing out ofmaterial by the treating gas flowing through the tube at efficientvelocities.

The fill of each tube affects the flow pattern of the 7 material and thebalance between heat transfer by conduction and treatment by the heatinggases. The fill may vary considerably, depending on the material, thetreatment, the form of agitating devices used, etc. In general, thefilled volume of each tube will average between about lpercent and30percent of the tube volume. There is usually some gradient in the fillfrom end to end of the tube, the fill at the upstream end being somewhatgreater than the fill at the downstream end. A dam with a height ofabout percent of the diameter of the tube has produced excellent controlcharacteristics for a variety of materials in a dryer constructed inaccordance with the invention.

Various forms of agitating devices may be employed in the apparatus, theform used being somewhat dependent on the material and the treatmentbeing performed. A gentle tumbling action with good surface exposure butonly a moderate degree of intermittent particle suspension is attainedwith an axial solid or hollow core pipe that extends part way down thecenter of each tube and has one or more external fins or vanes extendinggenerally radially and longitudinally of the tube. Advantageously, theagitating device extends upstream from the inlet end of each tube somedistance into the inlet zone of the shell, the projecting end aiding thefeed of material to each tube and providing beneficial aeration of thematerial in the inlet zone. A hollow core pipe may have holes at spacedlocations along its length for flow of materials and gases into and outof the interior of the pipe.

It will generally be advisable not to have any aerating devices in aregion near the downstream end of the tube. The dam element is aconstriction in the gas flow cross-section where gas flow velocityincreases, and the influence of the increased velocity extends somewhatupstream from the dam element. A lack of agitating devices near the endof the tube ensures maintenance of the desired layer of material behindthe darn element and restricts entrainment of material in the gas in theregion near the outlet where the material might be blown out by the morerapidly flowing gas.

Other forms of agitator systems may be employed. For example, severalcircumferentially spaced-apart U-shaped or L-shaped vanes extendinglengthwise of the tube and spaced from the tube wall with the cavity ofthe U" or L shape generally facing the tube wall lift material up andthen let it gently tumble off in free fall (intermittent suspension)back to the bottom of the tube. The spacing of such agitating vanes fromthe tube wall provides a large material-tube contact area for heattransfer. The shape, size, number, location and orientation of the vanescan be varied to provide desired agitating effects.

High efficiency of heat transfer between the tubes and the heating orcooling fluid in the closed chamber around the tubes is promoted bybaffling the flow in the chamber. Preferably, a baffle at the upstreamend of the chamber defines with the upstream tube sheet a fluid inletzone, the fluid being brought by a conduit to the inlet zone. A secondbaffle near the downstream tube sheet forms an outlet zone for thefluid. Annular throttling orifices in each baffle immediately aroundeach tube promote an annular flow stream for good heat transfer betweenthe fluid and the tubes.

Among the important advantages of the apparatus of the invention are anability to provide close control of a process and produce a preciselyconditioned product, even with difficult materials (e.g., broad sizedistribution, bound moisture, friable,sticky, etc.), high heat transferefficiency, and low power requirements. On the last point, because thematerial load is essentially balanced by distribution around therotating shell axis, high rates of rotation in the range of, say, from20 to 40 r.p.m., which provide highly effective agitation and promoteefficiency and enhance control capability, are attainable with verylittle horsepower input.

DESCRIPTION OF THE DRAWINGS For a better understanding of the inventionand a further description of preferred features and/variations of theapparatus of the invention, reference may be made to the followingdescription of exemplary embodiments, taken in conjunction with thefigures of the accompanying drawings, in which:

FIG. 1 is a side elevational view of one embodiment of the apparatus;

FIG. 2 is a side view in cross-section taken generally along adiametrical plane of the rotary part and some of the adjacent structureof the apparatus of FIG. 1, the view being on a slightly larger scalethan FIG. 1;

FIG. 3 is a side view in cross-section of one form of tube and agitatingstructure employed in the rotary section of the apparatus shown in FIGS.1 and 2, the view again being on a larger scale and having a portionbroken away;

FIG. 4A is an end view in cross-section of the inlet end of the tube ofFIG. 3, the view being taken generally along the lines 44 of FIG. 3 andin the direction of the arrows and being on a larger scale than FIG. 3;

FIGS. 48, 4C, 4D and 4E are diagrammatic illustrations showing the flowpattern of material treated in apparatus having tubes with agitatingdevices of the form illustrated in FIGS. 3 and 4A;

FIG. 5 is a cross-sectional view of the rotary part of the apparatus ofFIGS. 1 to 4, the view being broken away in two partial end sectionstaken generally along planes indicated generally by the lines 55 of FIG.2 and taken in the direction of the arrows;

FIG. 6 is an end sectional view of the rotary part of the apparatus ofFIGS. 1 to 5 taken at generally the outlet end along the lines 66 and inthe direction of the arrows in FIG. 2;

FIG. 7 is another end sectional view of the outlet end of the rotarypart of the apparatus of FIGS. 1 to 6, the view being taken generallyalong the lines 7-7 of FIG. 2 and in the direction of the arrows;

FIG. 8 is a cross-sectional view, taken generally along a diametricalplane, of another form of tube'for the apparatus; the tube having adifferent type of agitating device;

FIG. 9A is an end view in cross-section of the form of tube illustratedin FIG. 8, the view being taken generally along the lines 9A9A of FIG. 8and in the direction of the arrows;

FIGS. 98 to 9D are diagrammatic end sectional views showing the flowpattern of material in a tube with agitators of the form of FIGS. 8 and9A; A

FIG. 10 is a cross-sectional view taken generally along a diame'tricalplane of the exit end of a tube that is equipped with a screw-type offlow control dam;

FIG. 11 is an end view of the flow control dam illustrated in FIG. 10;

FIG. 12 is a side cross-sectional view of the outlet end part of a tubehaving another form of flow control dam; and

FIG. 13 is an end view of the flow control dam of FIG. 12.

DESCRIPTION OF EXEMPLARY EMBODIMENT Referring first to FIG. 1, aparticulate material to be treated in the apparatus of the invention issupplied at a controlled rate through an appropriate form of feeder,such as a screw-type feeder 10 shown to the left in the figure. In someinstances, it will be desirable to use an airlock type of feeder, suchas a rotary-valve type, for material sensitive to compression orextrusion. The outlet of the feeder extends through an end cover 12 thatis mounted in a fixed position on an appropriate supporting structure14. The embodiment of the-invention illustrated in the drawings anddescribed herein is a general purpose dryer, and FIG. 1 illustrates,schematically, an air heater 16, which is also mounted on the framestructure 14, that supplies hot air to the inlet end of the apparatusthrough the fixed end cover plate 12. Heated or cooled air, other gasesor vapors o'r ambient air may be supplied through the inlet opening inthe end cover plate 12. l

The fixed end cover plate 12 closes (and is sealed by a seal 13 to) theopen end ofa rotating cylindrical shell 18 in which the materialtreatment, in this case, drying, takes place. Spaced apart tires 20affixed to the outer surface of the shell 18 ride on supporting rollers22, and the shell 18 is driven in rotation through a chain drive 24 by amotor 26. The outlet end of the rotating shell, which is to the right inFIG. 1, is closed by a fixed end cover 28 that is appropriately mountedon another gas flow are conducted through a conduit branch 44 into acyclone 46 for separation, the particulate material separated in thecyclone being discharged from the lower end of the cyclone through aconduit 48 for outfeed through the rotary valve 42 and the gases beingtaken off from thetop of the cyclone by a blower 50. The cyclone or anyother form of separating system and apparatus for further handling ofthe solids and gases treated in the apparatus of the invention form nopart of the present invention and may be of various types that arewell-known to those skilled in the art. For example, the equipment mayemploy a closed-circuit gas recirculating system, such as when theapparatus is used in an inert atmosphere, or for solvent recovery.

portion 30 of the supporting framework and is sealed to the shell by aseal 31. The frame, which is designated generally by the referencenumeral 32, is supported at one end by a pivot block support 34 and atthe other end by a hydraulic jack 36 which can be driven to raise andlower the input end of the apparatus, relative to the output'end, andthereby vary the inclination of the apparatus to an appropriate extentto alter the rate of flow of material through the apparatus.

The particulate material treated in the dryer and the hot exhaust gasesare discharged from the apparatus through a conduit 38 leading outthrough the downstream end cover' plate 28. A lateral 40 on the conduitsystem takes the relatively larger particles of the material from theconduit and delivers them directly to a rotary-type valve 42 fordischarge. The major part of the gases and the fine particles ofmaterial entrained in the Closed-circuit systems will often havecondensers or scrubbers for drying out the recirculated gas and heatexchangers for reheating in the case of drying, chillers for cooling,and other types of ancillary equipment, the nature of which will dependupon the use to which the apparatus of the invention is being put.

Referring next to FIG. 2 of the drawings, the rotary part is dividedinto three sections, an inlet section designated generally by thereference numeral 52, a treatment section 54 and an outlet section 56.Lest it be misleading to term the section 54 a treatment section, it isappropriate to mention that a significant degree of treatment of thematerial occurs both in the inlet and outlet zones, as well as in theaforesaid treatment zone. The subdivision of the rotary part or shell'18 into the above-mentioned sections is provided by a pair oftransverse, longitudinally spaced-apart tube sheets 58 and 60. The tubesheets 58 and 60 are sealed to the outer walls of the shell and carry. aseries of spacedapart, longitudinally-extending tubes 62. The ends ofeach tube are sealed, such as by welding, to the tube sheets 58 and 60so that the space between the tube sheets 58 and 60 and outside of thetubes constitutes a closed chamber. As an optional feature, the centerportion of the chamber 64 contains a central tube 66, the ends of whichare blanked off by closures 68, for supplying and removing fluids to andfrom the chamber.

The closed chamber within the treating portion 54 of the shell 18receives, in the case of the apparatus employed as a dryer or heater, aheated fluid, such as hot water, hot oil or steam, that is conductedinto the chamber 64, circulated through the chamber and dischargedthrough a rotary union of any appropriate form installed in thedownstream end cover plate. The chamber may be built as a pressurevessel for operating at liquid or steam pressures well aboveatmospheric.

A heating fluid is supplied to the chamber through an inlet pipe 72connected to the union, passes through an annular space within an outerrotating conduit 74 of the union 70 and then is conducted through asupply pipe76 that extends through the center pipe 66 within the chamberto a point near the upstream end of the chamber, where it turnslaterally and extends out through the wall of the center tube 66 forrelease of the fluid into the chamber. Where a liquid is used, it isdesirable to provide baffles to control the flow of the liquid. In theillustrated embodiment, a baffle plate 80 distributes the fluid evenlythroughout the cross-section of the chamber 64 in the region thereofdownstream (or to the right relative to FIG. 2) of the baffle. The fluidflows through the center portion and out of the center portion of thechamber 64 through a second baffle plate 82. As may best be seen in theupper part of FIG.

of the drawings, each of the baffles (only the upstream baffle 80 isshown in FIG. 5) is formed with an annular throttling orifice 82 aroundeach tube. Accordingly, the baffles provide for a substantially uniformdistribution of heating fluid and for a flow of an annular curtain orstream of heating fluid along the outer surface of each tube 62.

The heating fluid is withdrawn from the chamber 64 through an outletpipe 84, the upstream end of which extends into the downstream end ofthe center tube 66 and then turns outwardly through the wall of the tube66 for communication with the chamber 64 and the downstream end of whichleads to the union 70. The fluid leaves the union through an outlet pipe86.

The lower portion of FIG. 5 illustrates, by a phantom line designated bythe reference numeral 98, an appropriate fill level in the bottom of theinlet section 52 for material fed into the apparatus by the feeder 10.The fill level line is drawn to represent the material free surface withthe shell rotating in operation. The fill level should be such that theexposed open ends of each tube are partly covered by the rolling bed ofparticulate material contained in the lower region of the inlet section52. The precise shape and the flow pattern of the body of material inthe inlet section will, of course, vary with the flow characteristics ofthe material and various other aspects of the operation of theequipment. The objective of the feed system, however, is to provide alayer of material that covers at least a part of the open end of eachtube so that the material flows into each tube as it successivelyrotates by the body of material. Meanwhile, the body of material isbeing rolled and turned by the natural action of the rotation of theshell. In addition, an appropriate system for inducing agitation of thematerial in the inlet section may be provided. Such a system may be partof the agitator structures associated with the tubes 62.

FIGS. 1 to 7 show one form of agitator structure for the apparatus ofthe invention. The agitator structure, as best seen in FIGS. 3, 4A, 5and 6, includes a hollow core pipe 100 extending axially through eachtube 62 and projecting back from thetube end some distance .into theinlet zone 52 (see FIG. 2). The upstream ends of the core pipes areclosed so that gas does not enter them at the upstream ends. Theportions of the core pipes that project back into the inlet zone 52assist in feeding the material and provide a degree of agitation in thebody or bed of material in the inlet zone, as should be evident fromFIG. 5; as each tube 62 rotates with the shell structure through therolling body of material in the inlet section, the projecting endportion of each core pipe 100 stirs and lifts and tends to create anopen area beneath it for stirring and aeration of the bed of material.

The core pipe 100 extends over most of the length of the tube and hasits axis coincident with the axis of the tube. A pair of fins or vanes104, which are secured to the outer wall of the core pipe 100, extendlongitudinally along most of the length of the core pipe and extendradially, in opposite directions from lengthwise lines diametricallyopposite each other on the core pipe 100. The outer edges of the vanes104 are spaced from the inner wall of the tube 62. The core pipe 100 andvanes 104 are mounted in each tube by support bars 106 near the ends ofthe core pipe. The support bars for the aerating structure fitrelatively loosely into the tube 62 so that the entire aeratingstructure may be relatively easily and quickly removed for cleaning, andfor cleaning of the tube, and then replaced in the tube. The entireaerating assembly is located and held in proper position in the tube bya retainer ring 107 that is common to all core pipes, is passed throughholes in each of the core pipes, and engages the upstream tube sheet 58,thereby keeping the aerating structures from being blown or carried bymaterial in a downstream direction in the tubes.

There are two sets of openings 108 along generally diametricallyopposite positions around the circumference of each core pipe. Each setof openings is immediately adjacent to one of the vanes 104, and the setof openings associated with one of the vanes is offset longitudinallyfrom the other set of openings associated with the other vane.

The flow pattern of material handled in the apparatus of FIGS. 1 to 7 isillustrated diagrammatically in FIGS. 4B to 4E. In each of thosefigures, the arrowed line designates the direction of rotation, and eachfigure illustrates a tube 62 with the vanes 104 oriented at a differentangular position and is thus indicative of different stages during onecycle of rotation of a given tube.

As each tube 62 rotates with the shell, the vanes 104 move relativelythrough the bed of material that accumulates in the lower part of thetube. The material has an inclined free surface that results from thecentrifugal and frictional forces generated upon rotation of the tube.Each vane picks up a body of material and carries it upwardly in atrough defined by the vane surface and a portion of the surface of thecore pipe 100 adjacent the vane (see FIG. 4B). The parts of the pickedup material that are near the holes 108 adjacent the vane that is thenmoving upwardly through the bed of material pass through the holes andenter the interior of the core pipe. Inasmuch as the holes through whichsuch material enter are opposite a solid wall portion of the core pipe,the material entering the interior of the core pipe is retained andtumbles in a general rolling manner across the lower portion of the corepipe. Gas moving through the tube also enters and leaves the core pipethrough the holes 108.

At the same time, the material within the core pipe is moving in adownstream direction by gravity forces resulting from an inclination ofthe axis of the rotary section and forces induced by the flow of gasesthrough same hole 108 through which it entered after 180 of rotation,but a portion of the material entering through a given hole 108 isretained in the core pipe and flows downstream in the core pipe until itreaches another hole 108, at which point it will drop out through thathole and be comingled with the bed of material in the bottom of the tube62.

In regions where there is no hole 108 immediately adjacent to a vane104, the body of material will be retained in the trough defined betweenthe vane and the adjacent part of the surface of the core pipe (seeFIGS. 4C and 4D). As a given vane passes beyond the position illustratedin FIG. 4B, the surface layer at the free surface of the body ofmaterial captured and lifted on the vane begins to roll off the corepipe and falls back to the bottom. From that point on, the materialgradually rolls off the core pipe and becomes temporarily suspended inthe gas flowing through the tube and then settles back to the bottom ofthe tube.

It should be evident from examining FIGS. 48 to 4E of the drawings thatthe form of aerating device employed in the embodiment of FIGS. 1 to 7of the drawings provides a gentle tumbling action with a moderate amountof free-falling or temporarily suspended material. Nonetheless, there isa substantial surface area exposure of the material to gases flowingthrough the tube. The lower portion of each tube remains covered by alayer of material at all times, that is at all orientations of theaerating structure. Accordingly, heat transfer between the material andthe tube walls is never interrupted, thereby efficiently employing theheat transfer capability of the tube walls. The high rate of rota- 'tionof the rotary section further enhances effective use of the heattransfer capability of the tubes and flowing gas by rapid cycling ofeach particle of material.

The gentle agitation and tumbling afforded by the form of aeratingdevice employed in the embodiment of FIGS. 1 to 7 provides a goodbalance between heat transfer from the tube walls into the material andheat and vapor transfer between the material and gas flowing through thetube. The agitating structure provides continuous, repeated cycling ofeach particle of material in the body of material being treated betweena free surface exposure to hot gases, a free-falling exposure to thegases and a contact engagement with a hot surface, either the surface ofthe tube or the surface of the core pipe or vanes.

Near the downstream end of each tube, the fill level is relatively low,and aeration devices provide only limited effectiveness. Accordingly,the aeration device does not extend to the downstream end of the tube 62but stops some distance from the end. Moreover, an important feature ofthe invention is the provision at the outlet end of each tube of aflow-control dam element. The height of the dam element is uniform alongthe circumference of the tube. The dam ensures the retention of alayerof material in the bottom of the tube, an aspect of the apparatus thathas been found to be extremely significant.

More particularly, a completely open tube end provides a relativelysmooth surface for material. to be blown out through the end of the tubeby gas flowing through the tube at an efficient velocity. Smallvariations in the characteristics of the material and the gas flowconditions can produce very significant variations in the amount of blowout of material in such an outlet. ln contrast,.the flow-control damprevents material from being blown out of the tube end and provides auniform layer of material at the outlet end which, in turn, controls theflowof material all the way back to the inlet end. Consequently, theflow-control dam plays a critical part in maintaining a uniform flowrate through each tube, all other things being equal.

The height of the dam may vary somewhat, depending upon the gradient ofthe fill level along the length of each tube and the extent to which theflow crosssection for gas flow may be reduced at the outlet end of eachtube. Very good results have been obtained with a dam having a height ofapproximately percent of the diameter of the tube.

One form of dam element, which is best seen in FIG. 3 of the drawings,is an annular, flat disc 114 that has a centrally located circularopening 116 and is affixed to a cylindrical sleeve 118, such as bywelding. The

sleeve is received within the downstream end portion of the tube 62 andhas a multiplicity of longitudinal slot that subdivide its free or innerendportion into a multiplicity of segments 122. The sleeve 118 is madeof a resilient material and the segments 122 are slots outwardlyslightly so that when the dam element 112 is installed, the resiliencyand geometry of the segments 122 provide firm frictional engagement withthe tube walls so that the dam element is held in place in the end ofthe tube 62. Nonetheless, the dam element may be readily removed forcleaning and for cleaning of the inside of the tubes 62.

An alternate form of flow-control dam for the outlet end of each tube isa screw form (see FIGS. 10 and 11) provided by a strip 124 of materialinstalled as a helix within a sleeve 126, the helical strip 124 havingat least one full pitch, and preferably somewhat in excess of one fullpitch. The screw form provides additional control in that it produces apositive feeding action and thus provides more direct control over theoutput of each tube and therefore control of throughput and retentiontime.

A third form of dam structure (shown in FIGS. 12 and 13) is composed ofthe resilient form of sleeve 128 and a series of annular segments 129that are longitudinally spaced-apart, and overlap each other. Thematerial can pass between the ends of those segments that are in a givenplane, but the segments in aggregate provide a dam effect against axialblow-out of material.

Upon leaving each tube, the material being treated falls into the bottomof the outlet zone 56 of the apparatus. Referring to FIGS. 2 and 7 ofthe drawings, the downstream end of the outlet zone 56 has amultiplicity of lifting cups 130 having concave surfaces facing in thedirection of rotation of the rotary section of the'apparatus. Thematerial in the bottom of the outlet zone 56 is picked up in theconcavity of each lifting cup 130 and is carried upwardly for dischargeinto an upwardly open outlet funnel 132. The funnel leads to an outletconduit section 134 and into the discharge conduit 38 (see FIG. 1).Gases, together with any fine material that may be entrained in thegases, leave .the apparatus through the same conduit section 134 anddischarge conduit 38 as the solid material picked up and removed by thelifting members 130.

FIGS. 8 and 9A through 9D illustrate another form of from structure thatmay be employed in a particulate material treating apparatus accordingto the invention.

The agitating structure shown in those figures comprises a multiplicityof longitudinally extending vanes mounted on a pair (or more) oflongitudinally spaced-apart, generally annular support rings 152. Thevanes extend back or upstream some distance into the inlet section andagitate the material in the inlet section to assist in feeding andprovide beneficial aeration. The vanes are located at an equal distancefrom the axis of the tube and equal distances fro each other and extendalong most of the length of each tube, though they do stop some distancefrom the downstream end. Each of the support members 152 includes anannular central portion 154 and a number of outwardly extending legportions 156a and 15611. The legs designated l56b extend outwardly intoengagement with the inner wall of the tube and serve as spacers orsupports for the entire agitating structure in the tube. The legsdesignated 1560 are somewhat shorter. All of the legs- 156a and 156 bare angularly related to the adjacent annular ring part 154 so as tomatch an obtuse angle defined between the outwardly facing surfaces ofthe two leg portions 150a and l50b of each vane. The vanes areappropriately secured, such as by spot welding, to each of the supportmembers. The supporting legs l56b of each of the support members 152 fitrelatively loosely within the tube so that the entire agitatingstructure in each tube may readily be removed for cleaning of theagitating structure and the tube.

As illustrated schematically in FIGS. 98 to 9D, each vane movesrelatively through the body of material in the lower portion of eachtube 62, picks up some of the material from that layer, carries itupwardly and gradually drops it over the edge of the leg 1568 in afreefalling cascade. As a given blade reaches approximately the 12o'clock position (see FIG. 9D), the material falling over the edge ofthat blade tends to drop onto the back of a blade two positions ahead ofthe 12 o'clock blade. The blade which that falling material impingesupon deflects the material and redrops it back into the bottom of thetube. In almost all instances, as a matter of fact, the material fallingfrom a blade in an upper position in the tube falls onto a blade in alower position and redistributes the flow of material for release backinto the bottom of the tube. The aerating device illustrated in FIGS. 8and 9A to 9D thus provides a substantial amount of freely cascadingmaterial, and all particles of material in the body of material beingtreated in each tube are cycled at frequent intervals through afree-falling cascade, a residence period in contact with a hot surface,such as either the surface of a blade or the wall of the tube, or atumbling or rolling flow along a layer of material falling off a vane.Such cycling of each particle of material provides a combination of heattransfer by conduction into the material from a hot surface and heat andvapor transfer by conduction and convection between the hot gasesconducted through the tubes and the exposed surface layers of bodies ofmaterial as well as the exposed particles in free-falling areas.

As mentioned above, the apparatus of the invention is highly versatile,and the mode of operation of apparatus of a particular design may becontrolled to permit that apparatus to handle a wide variety of specificprocess conditions. There is, of course, a great deal of knowledge inthe art concerning the processing of particulate material, and thoseskilled in the art will readily be able to determine, either bycalculations, by experimentation, or both, the appropriate treatmentconditions to be effected in apparatus constructed in accordance withthe invention.

Taking a dryer as an example, the two most important factors in drying amaterial are the particle size and the particle structure. These factorsare interrelated, except in the case when the material is relativelynonabsorbant and holds only surface moisture. Surface moisture isreadily evaporated, regardless of particle size, provided that thesurfaces of the particles are sufficiently exposed to hot gases andprovides that an appropriate mean temperature difference and mean vaporpressure difference between gas and solids exists. On the other hand,when the particle structure is dense and the particle contains internalor bound moisture,

the moisture must be diffused to the surface before it can beevaporated. The rate of diffusion varies considerably from one materialto another, but in a given material it is, of course, more difficult toachieve diffusion of bound moisture to the particle surface inrelatively larger size particles. The extent to which a materialcontains bound moisture and the rate of diffusion of the moisture to thesurface are, therefore, important factors that will be considered inestablishing drying conditions in a dryer of the invention.

Among other important variables that are susceptible of wide variationin establishing the conditions of the apparatus are the mean temperaturedifference between the gas and the solids and the means difference inthe vapor pressures, i.e., the difference between the partial vaporpressure and the vapor pressure at saturation at the surface temperatureof the solid. The temperature difference and vapor pressure differencemay be controlled in the apparatus, such as by controlling thetemperature and flow rate of gases in the apparatus.

The degree of aeration by gentle tumbling agitation of the materialtreated in apparatus according to the invention depends primarily on theparticle size and structure. In general, the smaller the particles beingtreated, the greater will be the need for aeration to ensure that thesurfaces of all particles are contacted by the gas. The need for arelatively high amount of agitation must be balanced against the flowrate and temperature to ensure that there is an appropriate temperaturedifference and vapor pressure difference in the operation of the systemso that an excessive amount of fine particles are not entrained andswept through the apparatus without being sufficiently dried. Ingeneral, however, relatively fine particles can be picked up and carriedout and at the same time be adequately dried, inasmuch as entrainedparticles are highly contacted by the gas and will dry rapidly in amanner resembling the very rapid drying attained in flash dryers. Formaterials having a wide range of particle size, for newly-formedagglomerates and for fragile or abrasive particles, a high amount ofagitation is generally detrimental. In treating such materials in theapparatus, a form of agitating structure providing only a relativelygentle tumbling or rolling action and a minimum of free-falling fallingwill be preferred and may be provided. In addition to employingdifferent forms of agitating structures in the apparatus, the rate ofrotation of the rotary section also materially affects the total amountof agitation of the material as it is processed through the apparatus.

Among the variables affecting the retention time of material in theapparatus are the form and dimensions of the flow-control dam, thevelocity of the gas moving through the tubes, the rate of rotation ofthe rotary section, and the degree of inclination of the axis of therotary section. In should be mentioned that the apparatus of theinvention provides a feeding action, even in a horizontal position,since that part of the material making at a given instant a free-falltends to be blown downstream by the gases flowing through the tube.Thus, the apparatus may, in some applications, be operated with its axisvery nearly horizontal. The ability to vary any of the variablesaffecting retention time, however, provides another important factor inthe versatility of the apparatus and in the ability to achieve excellentcontrol of operating conditions.

The embodiments of the invention described above are merely exemplary,and those skilled in the art will be able to make various variations andmodifications of the embodiments without departing from the spirit andscope of the invention. All such variations and modifications areintended to be included within the scope of the invention as defined inthe appended claims.

I claim:

1. Apparatus for treating (e.g., drying, heating, cooling or reacting)particulate material comprising a cylindrical shell mounted for rotationabout-its axis, means for rotating the shell, fixed end covers closingthe ends of the shell, first and second transverse tube sheets fixedwithin the shell at spaced-apart locations, the first tube sheet and oneend cover defining an inlet zone in the shell, the second tube sheet andthe other end cover defining an outlet zone in the shell, and the twotube sheets defining a closed chamber between them, means forintroducing the particulate material to be treated into the inletzone ata controlled rate, a multiplicity of tubes mounted in the tube sheets inspaced-apart relation, the tubes communicating the inlet zone with theoutlet zone for flow of the material and a gas therethrough, a materialflow-control darn element mounted in each tube adjacent the downstreamend thereof and providing a controlled fill of material in each tube,each dam element being a member extending circumferentially of andinwardly from the tube wall a uniform distance, means in each tube foragitating the material flowing therethrough, means for conducting a flowof gas through the tubes, means for conducting a flow of a heating orcooling fluid through the closed chamber outside the tubes for heatexchange with the tube walls, and means for removing the material andgas from the outlet zone of the apparatus.

2. Apparatus according to claim 1 and further comprising means in theinlet section of the apparatus for agitating the material receivedtherein.

3. Apparatus according to claim 2 wherein the agitating means in thetubes and the agitating means in the inlet section include commonelements. 1

4. Apparatus according to claim 1 wherein the means for agitating thematerial in each tube includes a core pipe element extending axiallythrough at least an upstream portion of each tube.

5. Apparatus according to claim 4 wherein each core pipe projects fromthe upstream end of the respective tube a substantial distance into theinlet zone thereby to agitate material in the inlet zone.

6. Apparatus according to claim 4 wherein the core pipe element hasopenings in the wall thereof for flow of gases and the material beingtreated between the interior of the core pipe element and the annularspace within the tube and outside of the core pipe element.

7 Apparatus according to claim 1 wherein the agitating means includes amultiplicity of vanes in each tube extending generally lengthwisethereof and spaced from each other and from the tube axis.

8. Apparatus according to claim 7 wherein the vanes are spaced from thewall of the tube.

9. Apparatus according to claim 7 wherein each vane includes incross-section first and second spaced-apart portions defining an obtuseangle between them thereby to define a cavity for reception and liftingof material.

10. Apparatus according to claim 9 wherein the vanes are generallyL-shaped in cross-section.

11. Apparatus according to claim 10 wherein the vanes extend upstreamfrom the tubes into the inlet section thereby to agitate materialreceived in the inlet section.

12. Apparatus according to claim 1 wherein a downstream end portion ofeach tube adjacent the flowcontrol dam element thereof is free ofagitating means thereby to restrict aeration in such end portion, permitan accumulation of material behind the dam element, and limitentrainment of material in the gas flow.

13. Apparatus according to claim 1 wherein the aqitating means includesan axially extending centrally located hollow core pipe element and atleast one vane mounted on the exterior of the core pipe element andextending generally radially outwardly from and longitudinally of thecore pipe element.

14. Apparatus according to claim 13 wherein the core pipe element hasspaced-apart openings in the wall thereof for flow of gases and thematerial being treated between the interior of the core pipe element andthe annular space within the tube and outside of the core pipe element.

15. Apparatus according to claim 14 wherein there is at least one pairof vanes, the vanes of said pair being located at diametrically oppositepositions on the core pipe element and wherein the core pipe elementopenings are located downstream, relative to the direction of rotationof the tube, from each vane, the openings associated with each vanebeing staggered lengthwise of the core pipe element such that materialpicked up by the vanes enters and leaves the core pipe element throughthe openings.

16. Apparatus according to claim 1 wherein the agitating means isremovably received within each tube so that it is readily removed forcleaning and for cleaning of the tubes.

17. Apparatus according to claim 1 wherein each flow-control dam elementis a substantially flat annular plate mounted with its major surfacessubstantially perpendicular to the axis of the tube.

18. Apparatus according to claim 1 wherein each flow-control element isa strip of material of uniform width disposed helically adjacent the endof the tubes.

19. Apparatus according to claim 1 wherein the flowcontrol dam elementincludes a multiplicity of longitudinally spaced-apart overlappingannular segments, each of which has its ends spaced from an adjacentelement and all of which in aggregation define an annular obstruction tolongitudinal material flow of essentially uniform height measuredradially inwardly from the tube wall.

20. Apparatus according to claim 1 wherein the dam element is removablyreceived in each tube so that it is readily removed for cleaning and forcleaning of the tubes.

21. Apparatus according to claim 1 wherein the means for conducting aflow of fluid through the closed chamber includes baffle plates disposedtransversely across the chamber, a first baffle plate being positionedadjacent the first tube sheet and defining therewith a fluid supply zoneand a second baffle plate being positioned adjacent the second tubesheet and defining therewith a fluid discharge zone, a fluid supplyconduit communicating with the supply zone for supply of fluid to thechamber, and a fluid discharge conduit communicating with the fluiddischarge zone for removal of fluid from the chamber.

22. Apparatus according to claim 21 wherein each baffle plate includesan annular fluid flow-control orifice around each tube for inducing anannular flow stream along each tube.

23. Apparatus according to claim 1 wherein the shell and end covers aremounted for adjustment of the inclination of the axis of the shell.

1. Apparatus for treating (e.g., drying, heating, cooling or reacting)particulate material comprising a cylindrical shell mounted for rotationabout its axis, means for rotating the shell, fixed end covers closingthe ends of the shell, first and second transverse tube sheets fixedwithin the shell at spacedapart locations, the first tube sheet and oneend cover defining an inlet zone in the shell, the second tube sheet andthe other end cover defining an outlet zone in the shell, and the twotube sheets defining a closed chamber between them, means forintroducing the particulate material to be treated into the inlet zoneat a controlled rate, a multiplicity of tubes mounted in the tube sheetsin spaced-apart relation, the tubes communicating the inlet zone withthe outlet zone for flow of the material and a gas therethrough, amaterial flow-control dam element mounted in each tube adjacent thedownstream end thereof and providing a controlled fill of material ineach tube, each dam element being a member extending circumferentiallyof and inwardly from the tube wall a uniform distance, means in eachtube for agitating the material flowing therethrough, means forconducting a flow of gas through the tubes, means for conducting a flowof a heating or cooling fluid through the closed chamber outside thetubes for heat exchange with the tube walls, and means for removing thematerial and gas from the outlet zone of the apparatus.
 2. Apparatusaccording to claim 1 and further comprising means in the inlet sectionof the apparatus for agitating the material received therein. 3.Apparatus according to claim 2 wherein the agitating means in the tubesand the agitating means in the inlet section include common elements. 4.Apparatus according to claim 1 wherein the means for agitating thematerial in each tube includes a core pipe element extending axiallythrough at least an upstream portion of each tube.
 5. Apparatusaccording to claim 4 wherein each core pipe projects from the upstreamend of the respective tube a substantial distance into the inlet zonethereby to agitate material in the inlet zone.
 6. Apparatus according toclaim 4 wherein the core pipe element has openings in the wall thereoffor flow of gases and the material being treated between the interior ofthe core pipe element and the annular space within the tube and outsideof the core pipe element.
 7. Apparatus according to claim 1 wherein theagitating means includes a multiplicity of vanes in each tube extendinggenerally lengthwise thereof and spaced from each other and from thetube axis.
 8. Apparatus according to claim 7 wherein the vanes arespaced from the wall of the tube.
 9. Apparatus according to claim 7wherein each vane includes in cross-section first and secondspaced-apart portions defining an obtuse angle between them thereby todefine a cavity for reception and lifting of material.
 10. Apparatusaccording to claim 9 wherein the vanes are generally L-shaped incross-section.
 11. Apparatus according to claim 10 wherein the vanesextend upstream from the tubes into the inlet section thereby to agitatematerial received in the inlet section.
 12. Apparatus according to claim1 wherein a downstream end portion of each tube adjacent theflow-control dam element thereof is free of agitating means thereby torestrict aeration in such end portion, permit an accumulation ofmaterial behind the dam element, and limit entrainment of material inthe gas flow.
 13. Apparatus according to claim 1 wherein the aqitatingmeans includes an axially extending centrally located hollow core pipeelement and at least one vane mounted on the exterior of the core pipeelement and extending generally radially outwardly from andlongitudinally of the core pipe element.
 14. Apparatus according toclaim 13 wherein the core pipe element has spaced-apart openings in thewall thereof for flow of gases and the material being treated betweenthe interior of the core pipe element and the annular space within thetube and outside of the core pipe element.
 15. Apparatus according toclaim 14 wherein there is at least one pair of vanes, the vanes of saidpair being located at diametrically opposite positionS on the core pipeelement and wherein the core pipe element openings are locateddownstream, relative to the direction of rotation of the tube, from eachvane, the openings associated with each vane being staggered lengthwiseof the core pipe element such that material picked up by the vanesenters and leaves the core pipe element through the openings. 16.Apparatus according to claim 1 wherein the agitating means is removablyreceived within each tube so that it is readily removed for cleaning andfor cleaning of the tubes.
 17. Apparatus according to claim 1 whereineach flow-control dam element is a substantially flat annular platemounted with its major surfaces substantially perpendicular to the axisof the tube.
 18. Apparatus according to claim 1 wherein eachflow-control element is a strip of material of uniform width disposedhelically adjacent the end of the tubes.
 19. Apparatus according toclaim 1 wherein the flow-control dam element includes a multiplicity oflongitudinally spaced-apart overlapping annular segments, each of whichhas its ends spaced from an adjacent element and all of which inaggregation define an annular obstruction to longitudinal material flowof essentially uniform height measured radially inwardly from the tubewall.
 20. Apparatus according to claim 1 wherein the dam element isremovably received in each tube so that it is readily removed forcleaning and for cleaning of the tubes.
 21. Apparatus according to claim1 wherein the means for conducting a flow of fluid through the closedchamber includes baffle plates disposed transversely across the chamber,a first baffle plate being positioned adjacent the first tube sheet anddefining therewith a fluid supply zone and a second baffle plate beingpositioned adjacent the second tube sheet and defining therewith a fluiddischarge zone, a fluid supply conduit communicating with the supplyzone for supply of fluid to the chamber, and a fluid discharge conduitcommunicating with the fluid discharge zone for removal of fluid fromthe chamber.
 22. Apparatus according to claim 21 wherein each baffleplate includes an annular fluid flow-control orifice around each tubefor inducing an annular flow stream along each tube.
 23. Apparatusaccording to claim 1 wherein the shell and end covers are mounted foradjustment of the inclination of the axis of the shell.